1. Field of the Invention
The invention relates to suspensions for vehicle seats and the like and, more particularly, relates to mechanized suspensions for supporting seats the unloaded height of which can preferably be adjusted.
2. Discussion of the Related Art
Vehicle seat suspensions are well known and typically include a base member which is fixed at least from vertical movement and a seat support member which is mounted on the base member so as to be vertically moveable with respect to the base member when a load is imposed on the seat. Such members often include devices for adjusting the unloaded distance between the base member and the seat support member. One such mechanism is disclosed in U.S. Pat. No. 4,125,242 to Meiller et al. The mechanism disclosed by Meiller et al. includes laterally opposed scissor arm mechanisms connecting the base and seat support members and biased by tension springs so as to urge the seat support member away from the base member. The scissor arm mechanisms deflect (against the force of the tension springs) when a load is imposed on the seat support member. This relative motion is permitted by relative motion between a cam connected to the scissor arm mechanisms and a cam follower connected to the tension springs, respectively. The unloaded height of the seat support member can be adjusted by operation of a ratchet mechanism connecting the scissor arm mechanisms to the cam.
The mechanism disclosed by Meiller et al. suffers from several drawbacks. For instance, the cam and associated support mechanisms are integral with the scissor arm mechanism. As a result, the entire weight of the seat support plate assembly and all articles supported thereon are supported by the scissor arm mechanisms. The resulting relatively high forces imposed on the suspension joints tend to increase the friction in the suspension.
Moreover, the arrangement of the cam, the cam follower, the extension springs, and the tension adjusters is such that, during operation of the suspension system, the handle for adjusting the tension in the extension springs moves in and out with respect to the suspension housing. The handle also has the potential to interfere with and cause discomfort to the legs of the operator.
The design of Meiller et al. also does not permit easy interchangeability of ratchet and spring assist height adjust mechanisms. Such a task would instead require a significant rearrangement of components. Moreover, because the cam and ratchet height adjust mechanism are integral with the scissor arm mechanism, these mechanisms cannot be independently serviced.
Another seat suspension system, disclosed by Brodersen et al. in U.S. Pat. No. 5,125,631, supports most of the weight of the seat support member by a central arm assembly, and incorporates scissor arm mechanisms only to provide lateral stability to the seat. Separate embodiments of this mechanism provide for height adjustment of the seat support member either through operation of a ratchet mechanism, which can be operated by lifting the seat support member, or through operation of a spring-assisted mechanism, which automatically raises an unloaded seat member upon actuation of a handle.
The cam operated suspension system of Brodersen et al. suffers from several drawbacks and disadvantages. For instance, the cam surfaces rotate about a point which produces a linear spring rate throughout the entire range of the suspension stroke. This system thus may be subject to "bottoming out" or complete collapse of the suspension. If such bottoming out is to be avoided, relatively sturdy bumpers or similar elements must be employed.
In addition, the arrangement of the tension adjust assembly supporting the primary extension springs drives all of the load through the front flange of the upper seat support, requiring the provision of additional structural members and thus increasing the complexity of the system.
The ratchet-type and spring-assisted height adjust mechanisms of Brodersen et al. also exhibit several disadvantages and drawbacks. For instance, the ratchet mechanism contains small parts that require accurate alignment in order to function properly. The spring-assisted height adjust mechanism incorporates a latch mechanism formed integral with the arms and cam mechanism and which is dependent in operation on the mass applied to the seat support of the suspension, as well as the compression spring applying lifting forces to the seat support member during height adjust operations. The latch mechanism is therefore relatively difficult to unlatch because at least some of the forces of the compression springs and all of the forces resulting from the mass on the seat support must be overcome. The height adjust mechanism is also relatively difficult to assemble because it is directly connected to the main tension springs for the seat suspension.